A typical option for supplying internal combustion engines with fuel is fuel injection systems which have a number of fuel injectors or fuel injection devices. At the moment, in the case of self-igniting internal combustion engines, high-pressure reservoir fuel injection systems or common rail systems are being used. The fuel injectors or fuel injection devices that can be supplied with fuel by means of a common rail system are controlled by means of magnetic valves or piezoactuators.
In the case of fuel injectors which are used in piezo common rail (PCR) systems, the control device is embodied as a piezo element. In this process, an injection valve component that is embodied needle-shaped can be controlled directly by changing the electric voltage at a piezoactuator. When current is applied to the piezoactuator, the piezoelectric crystal stack experiences for example a lengthening that disappears again when the current is no longer applied.
In the case of piezo common rail (PCR) injectors, a really high fuel leakage occurs via the needle guide at the nozzle. It is known that the leakage to a strong degree depends on the diameter of the guide and on the ring gap belonging to it between the nozzle needle and the nozzle body as well as on the fuel and the ring gap length. At the moment, manufacturing a smaller guide diameter, i.e. for example of less than 4 mm, is expensive. On the one hand, a leakage leads to a heating of the fuel. On the other hand, the leakage must be compensated for by means of a higher supply performance of the fuel pump. The leakage must therefore be minimized as far as possible. During operation, as a result of the elastic deformation in the needle guide with increasing fuel pressure, the ring gap of the PCR injector tends to become greater, which causes the increase in the leakage to be increased considerably.
In order to counter the occurrence of leaks, the nozzle needle, and the nozzle body have thus far been paired in order to achieve in this way a smaller clearance in the ring gap in the PCR injectors. However, in the case of future applications aiming for pressures of 1800 bar and higher, there is likely to be a further increase in the leakage.